PROJECT SUMMARY/ABSTRACT Epilepsy affects approximately 1% of the population and one in 200 children. Disruption in many epilepsy-related genes alters signaling mediated by the mechanistic target of rapamycin (mTOR) pathway, which has been implicated not only in epilepsy but also in brain malformations and autism. The mTOR complex 1 (mTORC1) coordinates cellular metabolism through growth factors and amino acids that operate on two converging parallel pathways. Growth factor activation of mTORC1 and regulation by the tuberous sclerosis complex (TSC) have demonstrated roles in the regulation of brain development and neuronal activity. In contrast, amino acid activation of mTORC1 and regulation by DEP domain-containing 5 (DEPDC5) are yet to be rigorously studied in the brain. Genetic variants in the DEPDC5 gene have been found in patients with epilepsy and structural alterations in brain development (i.e. malformations of cortical development) suggesting that its protein product DEPDC5 plays an important role in the brain. Several questions remain about the mechanisms by which DEPDC5 regulates mTORC1 in neurons and how this impacts brain development, including whether DEPDC5 regulates amino acid mediated mTORC1 signaling in neurons. Answering these questions may open the possibility of therapeutically modulating nutrient signaling as a treatment for epilepsy. This project will establish in vivo and in vitro models of Depdc5 deficiency and address a crucial knowledge gap by defining the impact of DEPDC5 loss on neuronal signaling and brain development. Recently, I generated a mouse mode with brain-specific Depdc5 loss that has several features similar to patients with DEPDC5-related epilepsy (Yuskaitis et al., Neurobiol Dis 2018). These mice have seizures, abnormal neurons with hyperactive mTORC1 activity, and die prematurely in adulthood of an unknown cause. The first aim of the proposed project is to determine 1) whether the brain-specific Depdc5 knockout mice die prematurely from seizures, and 2) whether the drug rapamycin (an mTORC1 inhibitor) can prolong survival and stop seizures of these mice. Second, I will investigate whether DEPDC5 loss affects nutrient signaling in neurons. Third, I will establish a novel mouse model to determine whether the timing of Depdc5 loss impacts epilepsy and brain development independently. The proposed research will provide essential insights into the mechanisms underlying brain development and identify potential treatments for epilepsy. My career goal is to become an independent neurogenetics scientist with a focus on using cellular and mouse models to discern the fundamental mechanisms underlying brain development and epileptogenesis. My proposal combines a focused research project, exceptional mentorship, and rich institutional resources at Boston Children's Hospital and Harvard Medical School, which provide a solid foundation for my transition into an independently funded physician-scientist during this award.